U.S. patent application number 14/671908 was filed with the patent office on 2016-04-28 for temperature compensated real-time clock.
This patent application is currently assigned to Maxim Integrated Products, Inc.. The applicant listed for this patent is Maxim Integrated Products, Inc.. Invention is credited to Nathan Theodore Hackett.
Application Number | 20160116515 14/671908 |
Document ID | / |
Family ID | 55698705 |
Filed Date | 2016-04-28 |
United States Patent
Application |
20160116515 |
Kind Code |
A1 |
Hackett; Nathan Theodore |
April 28, 2016 |
TEMPERATURE COMPENSATED REAL-TIME CLOCK
Abstract
A temperature compensated real-time clock systems and methods
can include: measuring a temperature with a temperature sensor;
detecting a temperature dependent frequency from an oscillator;
inputting the temperature and determining a temperature estimate
for the oscillator with an infinite impulse response filter; and
determining a compensation factor, for the oscillator.
Inventors: |
Hackett; Nathan Theodore;
(Corona, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Maxim Integrated Products, Inc. |
San Jose |
CA |
US |
|
|
Assignee: |
Maxim Integrated Products,
Inc.
San Jose
CA
|
Family ID: |
55698705 |
Appl. No.: |
14/671908 |
Filed: |
March 27, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62069170 |
Oct 27, 2014 |
|
|
|
Current U.S.
Class: |
368/202 |
Current CPC
Class: |
H04L 27/2338 20130101;
H03L 1/026 20130101; H03B 5/04 20130101; G01R 22/04 20130101; G01R
21/133 20130101; H03B 5/36 20130101 |
International
Class: |
G01R 22/04 20060101
G01R022/04 |
Claims
1. A method of real-time clock compensation comprising: measuring a
temperature with a temperature sensor; detecting a temperature
dependent frequency from an oscillator; inputting the temperature
and determining a temperature estimate for the oscillator with an
infinite impulse response filter; and determining a compensation
factor, for the oscillator.
2. The method of claim 1 wherein determining the temperature
estimate includes performing a transfer function with the infinite
impulse response filter for the temperature estimate as a function
of the temperature and treating the oscillator as a first thermal
mass on a first thermal gradient and treating the temperature
sensor as a second thermal mass on a second thermal gradient.
3. The method of claim 2 wherein determining the temperature
estimate includes assuming the first thermal gradient and the first
thermal mass are exposed to the same ambient temperature, assuming
the second thermal gradient and the second thermal mass are exposed
to the same ambient temperature, or assuming a combination
thereof.
4. The method of claim 2 wherein determining the temperature
estimate for the oscillator includes assuming that the first
thermal gradient is not the same as the second thermal gradient,
assuming that the first thermal mass is not the same as the second
thermal mass, or assuming a combination thereof.
5. The method of claim 1 wherein detecting the temperature
dependent frequency includes detecting the temperature dependent
frequency with a crystal oscillator, a tuning fork style quartz
crystal oscillator, or an oscillator operating in the 32 KHz
range.
6. The method of claim 1 wherein: measuring the temperature
includes measuring the temperature with discrete samples of the
temperature sensor; and determining the temperature estimate
includes determining the temperature estimate based on the discrete
samples of the temperature sensor.
7. The method of claim 1 further comprising adjusting a real-time
clock based on the compensation factor, adjusting the oscillator's
load capacitance based on the compensation factor, or a combination
thereof.
8. The method of claim 7 wherein adjusting the real-time clock
includes adjusting registers within the real-time clock, adjusting
a frequency recorded by the real-time clock, or a combination
thereof.
9. The method of claim 1 further comprising coupling a system on a
chip incorporating a real-time clock to a remote sensor for
measuring electricity usage and providing a time of day for the
electricity usage based on the real-time clock.
10. The method of claim 9 wherein coupling the system on a chip to
the remote sensor includes coupling the system on a chip to a
current transformer, shunt, Rogowski coil, or a combination
thereof.
11. A temperature compensated system comprising: a temperature
sensor configured to measure a temperature; an oscillator
configured to detect a temperature dependent frequency; an infinite
impulse response filter configured to determine a temperature
estimate for the oscillator from the temperature; and digital logic
configured to determine a compensation factor for the
oscillator.
12. The system of claim 11 wherein the infinite impulse response
filter is configured to determine the temperature estimate by
performing a transfer function for the temperature estimate as a
function of the temperature and treating the oscillator as a first
thermal mass on a first thermal gradient and treating the
temperature sensor as a second thermal mass on a second thermal
gradient.
13. The system of claim 12 wherein the infinite impulse response
filter is configured to determine the temperature estimate by
assuming the first thermal gradient and the first thermal mass are
exposed to the same ambient temperature, assuming the second
thermal gradient and the second thermal mass are exposed to the
same ambient temperature, or assuming a combination thereof.
14. The system of claim 12 wherein the infinite impulse response
filter is configured to determine the temperature estimate by
assuming that the first thermal gradient is not the same as the
second thermal gradient, assuming that the first thermal mass is
not the same as the second thermal mass, or assuming a combination
thereof.
15. The system of claim 11 wherein the oscillator is a crystal
oscillator, a tuning fork style quartz crystal oscillator, or an
oscillator operating in the 32 KHz range.
16. The system of claim 11 wherein: the temperature sensor is
configured to measure the temperature with discrete samples; and
the infinite impulse response filter is configured to determine the
temperature estimate based on the discrete samples.
17. The system of claim 11 further comprising a real-time clock
configured to be adjusted based on the compensation factor, a load
capacitance of the oscillator is configured to be adjusted based on
the compensation factor, or a combination thereof.
18. The system of claim 17 wherein the real-time clock is
configured to be adjusted by adjusting registers within the
real-time clock, adjusting a frequency recorded by the real-time
clock, or a combination thereof.
19. The system of claim 11 further comprising a system on a chip
having a real-time clock coupled to a remote sensor for measuring
electricity usage and providing a time of day for the electricity
usage based on the real-time clock.
20. The system of claim 19 wherein the system on a chip is coupled
to a current transformer, shunt, Rogowski coil, or a combination
thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This claims priority benefit to all common subject matter of
U.S. Provisional Patent Application No. 62/069,170 filed Oct. 27,
2014; the content of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] This disclosure relates to real-time clocks, more
particularly to real-time clocks with crystal oscillator
temperature compensation.
BACKGROUND
[0003] The sophistication and complexity of the electrical power
grid has grown to include electricity meters that incorporate
timing functions for billing metrics. Timing functions provide
greater precision for consumers and providers by allowing increased
ability to manage costs. For example, timing functionality is
useful in "time-of-use" metering where the rate for energy can
change depending on the time of day the energy is used.
[0004] Meters employing time-of-use metering employ a real time
clock that is often based on a precision timing crystal. In some
applications the precision timing crystal is a tuning fork style
quartz crystal oscillator. The frequency of this crystal oscillator
is a function of temperature. A temperature sensor is sometimes
used to determine a correction factor for keeping the real time
clock accurate.
[0005] Temperature readings from these sensors, however, do not
directly measure the temperature of the crystal oscillator, and
correction factors based on these measurements can be inaccurate
and introduce compensation errors. There are industry standards for
accuracy of the real time clock in utility meters. In particular,
ANSI C12.1-2001 requirements for real time clock accuracy are two
minutes per week or 200 ppm over a temperature range of 30.degree.
C. to 70.degree. C. Some utilities require greater accuracies such
as one minute per month or 23 ppm at temperatures of 30.degree. C.
and 40.degree. C.
[0006] As industry standards for clock accuracy and variation
across temperature become increasingly tighter, real time clock
accuracy becomes an ever more important competitive feature and
market differentiator for electric meter real time clocks. Previous
solutions, that attempted to provide greater accuracy in
identifying accurate correction factors, include adding a time
delay to the temperature measurement before it is used to
compensate the real time clock. Adding a time delay can provide a
more accurate correction factor than an uncompensated temperature
measurement; however, a time delay is an incomplete solution as it
introduces compensation errors when ambient temperature shifts are
rapid.
[0007] Solutions have been long sought but prior developments have
not taught or suggested any complete solutions, and solutions to
these problems have long eluded those skilled in the art. Thus
there remains a considerable need for devices and methods that can
provide accurate temperature correction factors for real time
clocks.
SUMMARY
[0008] A temperature compensated real-time clock providing
significantly increased accuracy is disclosed along with methods of
manufacture, operation, and implementation. The temperature
compensated real-time clock can include: measuring a temperature
with a temperature sensor; detecting a temperature dependent
frequency from an oscillator; inputting the temperature and
determining a temperature estimate for the oscillator with an
infinite impulse response filter; and determining a compensation
factor, for the oscillator.
[0009] It is disclosed that determining the temperature estimate
for the oscillator with the infinite impulse response filter
includes determining the temperature estimate for the oscillator
with the infinite impulse response filter performing a transfer
function for the temperature estimate as a function of the
temperature and treating the oscillator as a first thermal mass on
a first thermal gradient and treating the temperature sensor as a
second thermal mass on a second thermal gradient.
[0010] It is disclosed that detecting the temperature dependent
frequency can include detecting the temperature dependent frequency
with: a crystal oscillator; a tuning fork style quartz crystal
oscillator; or an oscillator operating in the 32 KHz range.
[0011] It is disclosed that determining the temperature estimate
for the oscillator includes: assuming the first thermal gradient
and the first thermal mass are exposed to the same ambient
temperature; assuming the second thermal gradient and the second
thermal mass are exposed to the same ambient temperature; or a
combination thereof.
[0012] It is disclosed that determining the temperature estimate
for the oscillator includes: assuming that the first thermal
gradient is not the same as the second thermal gradient; assuming
that the first thermal mass is not the same as the second thermal
mass; or a combination thereof.
[0013] It is disclosed measuring the temperature is measured with
discrete samples of the temperature sensor and that determining the
temperature estimate is based on the discrete samples of the
temperature sensor.
[0014] It is further disclosed that methods of operation, and
implementation of the temperature compensated real-time clock can
include adjusting the real-time clock based on the compensation
factor, adjusting the oscillator's load capacitance based on the
compensation factor, or a combination thereof. It is disclosed that
adjusting the real-time clock can include adjusting registers
within the real-time clock, or adjusting the frequency recorded by
the real-time clock.
[0015] It is disclosed that determining a compensation factor, with
digital logic for the oscillator can include determining the
compensation factor from a table correlating a frequency of the
oscillator with a temperature of the oscillator, from an equation
describing the compensation factor as a function of the temperature
of the oscillator, or a combination thereof.
[0016] It is further disclosed that methods of manufacture,
operation, and implementation of the temperature compensated
real-time clock can include incorporating the temperature sensor,
the real-time clock, the digital logic, the infinite impulse
response filter within a system on a chip; and coupling the
oscillator to the system on a chip, the oscillator contained in a
separate vacuum sealed package.
[0017] It is further disclosed that methods of manufacture,
operation, and implementation of the temperature compensated
real-time clock can include coupling the system on a chip
incorporating the real-time clock to remote sensors for measuring
electricity usage and providing a time of day for the electricity
usage based on the temperature compensated real-time clock. It is
disclosed that the remote sensors can be a current transformer,
shunt, Rogowski coil, or a combination thereof.
[0018] Other contemplated embodiments can include objects,
features, aspects, and advantages in addition to or in place of
those mentioned above. These objects, features, aspects, and
advantages of the embodiments will become more apparent from the
following detailed description, along with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The temperature compensated real-time clock is illustrated
in the figures of the accompanying drawings which are meant to be
exemplary and not limiting, in which like reference numerals are
intended to refer to like components, and in which:
[0020] FIG. 1 is a block diagram of an embodiment of the
temperature compensated real-time clock.
[0021] FIG. 2 is a thermal model of the temperature sensor of FIG.
1.
[0022] FIG. 3 is a thermal model of the crystal oscillator of FIG.
1.
[0023] FIG. 4 is a schematic view of the infinite impulse response
filter of FIG. 1.
[0024] FIG. 5 is a block diagram of temperature compensation
components of FIG. 1.
[0025] FIG. 6 is a temperature chart for the temperature
compensated real-time clock of FIG. 1.
DETAILED DESCRIPTION
[0026] In the following description, reference is made to the
accompanying drawings that form a part hereof, and in which are
shown by way of illustration, embodiments in which the temperature
compensated real-time clock may be practiced. It is to be
understood that other embodiments may be utilized and structural
changes may be made without departing from the scope of the
temperature compensated real-time clock.
[0027] The temperature compensated real-time clock is described in
sufficient detail to enable those skilled in the art to make and
use the temperature compensated real-time clock and provide
numerous specific details to give a thorough understanding of the
temperature compensated real-time clock; however, it will be
apparent that the temperature compensated real-time clock may be
practiced without these specific details.
[0028] In order to avoid obscuring the temperature compensated
real-time clock, some well-known system configurations are not
disclosed in detail. Likewise, the drawings showing embodiments of
the system are semi-diagrammatic and not to scale and,
particularly, some of the dimensions are for the clarity of
presentation and are shown greatly exaggerated in the drawing
FIGS.
[0029] Referring now to FIG. 1, therein is shown a block diagram of
an embodiment of the temperature compensated real-time clock 100.
The temperature compensated real-time clock 100 is shown having a
system on a chip (SOC 102), coupled to a power transmission line
104. The SOC 102 can further be coupled to a pulse transformer 106
and to a remote IC 108 for isolating remote sensors 110 from the
SOC 102 that are monitoring the power transmission line 104.
Further, the SOC 102 includes a crystal oscillator 112 coupled
thereto.
[0030] The SOC 102 can be a single-phase electricity meter that
incorporates a microcontroller core 114, a compute engine (CE 116),
and remote interfaces 118. The remote interfaces 118 can couple the
remote sensors 110 to the SOC 102 through the remote IC 108.
[0031] The SOC 102 can further include analog to digital converters
(ADCs 120), such as delta-sigma ADCs, for measuring current
channels and voltage channels. The CE 116 can be a fixed-point
compute engine and can processes the ADCs 120 samples.
[0032] The code for the CE 116 resides in CE memory 122 and can be
shared with the microcontroller core 114. The microcontroller core
114 is further depicted having dedicated microcontroller memory
123.
[0033] The ADCs 120 can be configured to monitor environmental
signals including magnetic fields, or varying AC fields induced by
nearby power lines or the power transmission line 104. The remote
interfaces 118 may support channels assigned to measure line
voltage, line current, and neutral current, plus any other analog
signal of interest. It is contemplated that the remote interfaces
118 can be self-contained and provide inherent isolation to protect
the SOC 102 from the power transmission line 104 potentials. The
remote sensors 110 that can be connected to the SOC 102, via the
remote interfaces 118, can include current transformers, shunts, or
Rogowski coils.
[0034] The CE 116 of the SOC 102 can be used to process metrology
samples from the remote interfaces 118 and perform calculations on
the measurements, for example, real energy and reactive energy, as
well as volt-ampere hours for four-quadrant metering. The
measurements from the CE 116 can be accessed by the microcontroller
core 114, processed further, and output to peripheral devices 124
available to the microcontroller core 114 and coupled to the SOC
102 through device interfaces 126. Peripheral devices 124 coupled
to the SOC 102 through the device interface 126 can include serial
memory devices and complex display subsystems.
[0035] The SOC 102 can further include a real-time clock (RTC 128)
to record time-of-use metering information for multi-rate
applications. The RTC 128 can provide a time-stamp for the
measurements or other events including tamper events. The RTC 128
can use the crystal oscillator 112, coupled to the SOC 102, as a
frequency reference. The crystal oscillator 112 can provide a
temperature dependent frequency.
[0036] The crystal oscillator 112 can be, for example, a
tuning-fork-type crystal oscillator 112. The crystal oscillator 112
is typically contained within a vacuum sealed package external to
the SOC 102. The frequency supplied by the crystal oscillator 112
to the SOC 102 can be multiplied with a phase-locked loop 130 to
provide clocking for the CE 116 and the microcontroller core 114
along with other clocks required by the SOC 102.
[0037] The SOC 102 can further include temperature compensation
components. The temperature compensation components can include a
temperature sensor 132, which allows for a temperature-correction
mechanism that can guarantee conformance to accuracy standards over
temperature. The temperature compensation components implemented in
the present depiction of the temperature compensated real-time
clock can further include an infinite impulse response filter 134.
As used herein the infinite impulse response filter 134 is defined
as an impulse response filter including feedback.
[0038] The infinite impulse response filter 134 can be used to
estimate the actual temperature of the crystal oscillator 112 based
on input from the temperature sensor 132 and thermal models of the
temperature sensor 132 and the crystal oscillator 112, as discussed
in further detail below. The RTC 128 can be adjusted based on the
infinite impulse response filter 134 estimate and the time of day
can be output through the device interfaces 126.
[0039] The infinite impulse response filter 134 is depicted as an
independent functional block implemented in digital logic; however,
it is contemplated that the infinite impulse response filter 134
could be software or firmware for example running on the
microcontroller core 114. It is contemplated that the infinite
impulse response filter 134 is implemented in digital logic whether
as an independent functional block or as implemented with software
or firmware in the digital logic of a processor such as the
microcontroller core 114.
[0040] In the present embodiment of the temperature compensated
real-time clock 100, the temperature sensor 132 is much more
responsive to ambient temperature than the crystal oscillator 112,
due to the crystal oscillator's 112 isolation within a vacuum
sealed package. It has been discovered that the infinite impulse
response filter 134 can be implemented to provide an exceedingly
accurate model of the actual temperature of the crystal oscillator
112 based on the temperature sensor's 132 measurements. The RTC 128
can then be adjusted or compensated without adjustment and
compensation errors allowing the temperature compensated real-time
clock 100 to meet stringent governmental regulations and provide
greater accuracy in a highly competitive market.
[0041] Referring now to FIG. 2, therein is shown a thermal model of
the temperature sensor 132 of FIG. 1. The thermal model can include
a thermal gradient model 202 and a thermal mass model 204 coupled
to the end of the thermal gradient 202.
[0042] The thermal model of the temperature sensor 132 is shown
with an ambient temperature T.sub.A at one end of the thermal
gradient model 202 opposite from the thermal mass model 204. The
thermal model of the temperature sensor 132 is further shown with a
sensor temperature T.sub.S at a different end of the thermal
gradient model 202 near the thermal mass model 204.
[0043] The thermal gradient model 202 can be described using the
one-dimensional form of Fourier's law of thermal conduction given
by Equation 1:
q = K T x Equation 1 ##EQU00001##
[0044] Here, q is the local heat flux density equivalent to the
heat per unit area, and its vector. K is the material's thermal
conductivity. dT/dx is the thermal gradient in the direction of the
flow. The thermal mass model 204 can be approximated by an equation
assuming a uniform composition given by Equation 2:
q = mC p T t Equation 2 ##EQU00002##
[0045] Here, m is the mass of the body and C.sub.p is the isobaric
specific heat capacity of the material averaged over the relevant
temperature range. For bodies composed of numerous different
materials, the thermal masses for the different components can be
added together. The steady state heat transfer through the thermal
gradient model 202 and the thermal mass model 204 can be described
by Equation 3:
- K d [ T - T A ] = mC p T t Equation 3 ##EQU00003##
[0046] Equation 3 can be rewritten as:
T A - T = mC p d K T t Equation 4 ##EQU00004##
[0047] The resulting ordinary first order differential equation
is:
T A .alpha. - T .alpha. = T ' Equation 5 ##EQU00005##
[0048] Here, .alpha. represents thermal diffusivity divided by the
distance over which the heat has to diffuse. Thermal diffusivity is
the thermal conductivity divided by mass and specific heat
capacity. It is contemplated that .alpha. can represent a composite
value derived from the various different materials actually
involved in the real system, not just in terms of thermal mass but
also thermal conductivity and material thicknesses. Equation 5
rewritten specifically to describe the temperature sensor 132
is:
T S ' = T A .alpha. S - T S .alpha. S Equation 6 ##EQU00006##
[0049] Referring now to FIG. 3, therein is shown a thermal model of
the crystal oscillator 112 of FIG. 1. The thermal model can include
a thermal gradient model 302 and a thermal mass model 304 coupled
to the end of the thermal gradient model 302.
[0050] The thermal model of the crystal oscillator 112 is shown
with an ambient temperature T.sub.A at one end of the thermal
gradient model 302 opposite from the thermal mass model 304. The
thermal model of the crystal oscillator 112 is further shown with a
crystal temperature T.sub.X at a different end of the thermal
gradient model 302 near the thermal mass model 304.
[0051] The thermal gradient model 302 and the thermal mass model
304 can be described using Equation 1 and Equation 2, respectively.
Equation 1 and Equation 2 assume that both the thermal gradient
model 202 for the temperature sensor 132 of FIG. 1 and the thermal
gradient model 302 for the crystal oscillator 112 are exposed to
the same ambient temperature T.sub.A. The resulting ordinary first
order differential equation describing the heat transfer through
the thermal gradient model 302 and the thermal mass model 304 of
the crystal oscillator 112 is:
T X ' = T A .alpha. X - T X .alpha. X Equation 7 ##EQU00007##
[0052] Although the thermal gradient model 302 and the thermal mass
model 304 of the crystal oscillator 112, and the thermal gradient
model 202 and the thermal mass model 204 of the temperature sensor
132, are described as ordinary first order differential equations
using only a single thermal mass and thermal gradient for either
the temperature sensor 132 or the crystal oscillator 112, it is
contemplated that the thermal models could include multiple
gradients and masses having unique properties. Further it is
contemplated that the thermal models could be described as higher
order differential equations.
[0053] It has been discovered that using Equations 6 and 7 to model
potentially different thermal conductivity through the thermal
gradient model 202 of the temperature sensor 132 and the thermal
gradient model 302 of the crystal oscillator 112 provide a much
more accurate estimate of the actual temperature of the crystal
oscillator 112 and allow for more precise compensation or
adjustments. Further, it has been discovered that using Equations 6
and 7 to model potentially different thermal masses with the
thermal mass model 204 and the thermal mass model 304 further
enhance the accuracy of the temperature estimate of the crystal
oscillator 112 allow for even more precise compensation or
adjustments.
[0054] Referring now to FIG. 4, therein is shown a schematic view
of the infinite impulse response filter 134 of FIG. 1. The infinite
impulse response filter 134 can be designed by determining a
transfer function for the crystal temperature as a function of the
chip temperature.
[0055] First, the ordinary first order differential equations for
the temperature sensor 132 and the crystal oscillator 112 are
solved for the crystal temperature T.sub.X using the Laplace
method:
[ T X ] = 1 + .alpha. S S 1 + .alpha. X S [ T S ] Equation 8
##EQU00008##
[0056] The continuous time transfer function H(s) mapping the
Laplace transform of the input to the Laplace transform of the
output for converting sensor temperature into crystal temperature
is:
H ( S ) = 1 + .alpha. S S 1 + .alpha. X S Equaiton 9
##EQU00009##
[0057] A discrete time transfer function can be derived from the
continuous time transfer function using the z-transform
providing:
H [ z ] = 1 + .alpha. S - .alpha. S z - 1 1 + .alpha. X - .alpha. X
z - 1 Equation 10 ##EQU00010##
[0058] A difference equation can be derived from the discrete time
transfer function:
T E = T X [ n ] = ( 1 1 + .alpha. X ) ( ( 1 + .alpha. S ) T S [ n ]
- .alpha. S T S [ n - 1 ] + .alpha. X T X [ n - 1 ] ) Equation 11
##EQU00011##
[0059] The infinite impulse response filter 134 is described by
Equation 11. The delays of Equation 11, or the (n-1) are shown by
the delay block z.sup.-1. The operations on the thermal diffusivity
of both the temperature sensor 132 and the crystal oscillator 112
are also shown.
[0060] The output of the infinite impulse response filter 134 is an
estimated temperature T.sub.E of the crystal oscillator 112. It has
been discovered that implementing the infinite impulse response
filter 134 provides exceptional speed for providing the estimated
temperature T.sub.E of the crystal oscillator 112 based on the
sensor temperature T.sub.S of the temperature sensor 132.
[0061] Referring now to FIG. 5, therein is shown a block diagram of
temperature compensation components 502 for the real-time clock 128
of FIG. 1. The temperature compensation components 502 can include
the temperature sensor 132, the infinite impulse response filter
134, the RTC 128, and the crystal oscillator 112.
[0062] The crystal oscillator 112 of the temperature compensation
components 502 is shown with the crystal oscillator 112 operating
at 32 KHz. The crystal oscillator's 112 frequency can be
compensated based on the temperature estimate T.sub.E of the actual
crystal temperature T.sub.S using the infinite impulse response
filter 134.
[0063] The resultant temperature estimate T.sub.E from the infinite
impulse response filter 134 has been discovered to be highly
accurate. The estimated temperature T.sub.E from the infinite
impulse response filter 134 can be fed into RTC calibration logic
504 residing within the RTC 128.
[0064] The RTC calibration logic 504 can correlate the estimated
temperature from the infinite impulse response filter 134 with
compensation factor from a correlation table for the crystal
oscillator 112. The RTC calibration logic 504 can further calculate
the compensation factor based on the estimated temperature T.sub.E
from the infinite impulse response filter 134 using an equation.
The frequency from the crystal oscillator 112 can then be recorded
by registers within the RTC 128 at a modified or augmented rate as
the RTC logic 504 digitally adjusts the way the frequency of the
crystal oscillator 112 is recorded by registers within the RTC
128.
[0065] Adjusting the recording of the crystal oscillator's 112
frequency based on the accurate temperature estimate T.sub.E of the
infinite impulse response filter 134 allows the RTC 128 to provide
a highly accurate account of the time of day. It is contemplated
that an adjustment mechanism that adjusts the frequency of the
crystal oscillator 112 can also be used, such as adjusting the
crystal oscillator's 112 load capacitance.
[0066] Referring now to FIG. 6, therein is shown a temperature
chart for the temperature compensated real-time clock 100 of FIG.
1. The temperature chart is shown depicting the performance of the
infinite impulse response filter 134. The Y-axis is temperature,
the X-axis is time, the T.sub.A trace is the ambient temperature,
the T.sub.S trace is the sensor temperature, the T.sub.X trace is
the crystal temperature and the T.sub.E trace is the estimated
crystal temperature based on discrete samples of the sensor
temperature.
[0067] Thus, it has been discovered that the temperature
compensated real-time clock furnishes important and heretofore
unknown and unavailable solutions, capabilities, and functional
aspects. The resulting configurations are straightforward,
cost-effective, uncomplicated, highly versatile, accurate,
sensitive, and effective, and can be implemented by adapting known
components for ready, efficient, and economical manufacturing,
application, and utilization.
[0068] While the temperature compensated real-time clock has been
described in conjunction with a specific best mode, it is to be
understood that many alternatives, modifications, and variations
will be apparent to those skilled in the art in light of the
preceding description. Accordingly, it is intended to embrace all
such alternatives, modifications, and variations, which fall within
the scope of the included claims. All matters set forth herein or
shown in the accompanying drawings are to be interpreted in an
illustrative and non-limiting sense.
* * * * *